Heat responsive actuating device



May 11, 1954 1 E. MGCABE HEAT RESPONSIVE ACTUATING DEVICE Filed Nov. l5,1949 Patented May 11,1954

UNITED STATES PATENT OFFICE 8 Claims.

This invention relates to a new and improved heat responsive actuatingdevice and more particularly to an electric switch in which saidactuating device is incorporated for the purpose of opening and closingsaid switch under the iniiuence of varying conditions of applied heat.

The actuating device is designed to impart substantial amounts ofmovement upon heat variation with the movement following promptly uponsuch heat variation. 'I'he source of heat to which the device may beresponsive for operation may be that emanating from light rays which areabsorbed by a portion of the device to transmute the energy carried bythe rays into heat, or from local heating coils or the like or by acombination of these or other means.

The structure of my present invention constitutes an improvement overthe operating structures shown in my prior Patents Numbers 2,149,853 ofMarch '7, 1939; 2,159,392 of May 23, 1939; 2,162,098 of June 13, 1939,and 2,325,785 of August 3, 1943.

Heretofore, as disclosed in the above mentioned patents, bi-metalliccoils or strips have served as the heat responsive actuating elements ofgenerally similar devices and, with such means, it was necessary toprovide means to compensate for ambient temperature changes. This isparticularly true in view of certain of the specic uses for which thedevices are designed and intended. For example, in certain uses, thedevices may be associated with oil burners and with re boxes heated bysuch burners where the ambient temperature may be much higher with theburner operating than after sustained periods with the burner out ofoperation. The device is not designed to operate upon such gradualchanges in ambient temperature but to operate rapidly upon quick changessuch, for example, as the change in heat energy derived from the lightrays of a burner flame, which heat energy changes instantly when thellame is ignited or goes out. Another application, for example, is wherethe device is used to operate a signal or various combustion controlmeans upon indications of smoke density. Here, light may be directedfrom a light source across a flue through which the products ofcombustion pass and rapid control is desired upon changes in smokedensities independently of stack temperatures. Such stack temperaturesmay modify widely the ambient temperatures at the location of the deviceof the present invention. Further, it has been found as a practicalmatter in striving for sensitivity of response, which involvessubstantial travel of a moving member upon relatively small temperaturechanges, that bi-metallic members assumed proportions detrimental tostability and permanence of operating adjustments. While successfuldevices of the bi-metallic type, following the teachings of the abovementioned patents, have been produced and used, the need for more ruggedstructures and the desire for the elimination of ambient temperaturecompensation, both from the standpoint of simplifying the structures aswell as eliminating the effect of such means during the process ofmanufacture and adjustment of the device for service, has been evident.Also, greater sensitivity in the time of response of the heat responsiveelement to the presence and absence of heat has been desired than hasbeen attainable in structures employing bi-metal, such speed ofoperation being desirable in mechanical devices to enable their use forcertain control purposes now precluding the use of the slow actingmechanical type of devices at present available.

In its preferred form, the operating structure will be formed of metalcharacterized by a high temperature coeicient of ,expansion and lowthermal conductivity, both of which properties contribute towardsmeeting the desired objectives. One commercial alloy having thesecharacteristics is Chace No. '772 manganese base alloy, but it will beunderstood that the present invention does not reside in the specicmetal and that any suitable material may be used.

In utilizing light to actuate the present mechanism, the device operateson the basic principle that light waves can be transmuted into heat andthis heat is utilized in the present invention to cause movement of theacutated member, which may take the form of a movable switch contact.The switch contact will be opened or closed in response to the presenceor absence of light which may be focused on the heat responsive elementof the mechanism. An electric switch so actuated has utility, forexample, in serving to indicate smoke conditions arising from impropercombustion Within a furnace. Another example of its use is an en elementin the safety controls employed in systems for control of uid fuelburners. In the latter use, this switch construction may provide both astarting circuit and a maintaining circuit, the latter being held closedby the presence of light resulting from apparatus such, for example, asa fuel burner, which is capable of producing a source of light rays uponclosure of the switch contact for the starting circuit. A switch of thistype iinds its specific use in conjunction with control apparatus forcontrol of fluid burners as disclosed in my copend application SerialNo. 130, 896 led December' 3, 1949, entitled Fuel Burner Control.

As previously stated, this switch may also find use in connection withthe control of combustion based on variations in smoke density, theswitch being actuated by abnormal smoke ccnditions. To render the deviceuseful in some applications of smoke control, it may be desirable thatthe switch be sensitive to quite small changes in the amount oi light sothat the presence of small amounts of smoke or of small variations insmoke density may be suiiicient to interrupt or decrease the light raysenough to effect an opening of the switch circuit. Since the amount ofheat energy needed to maintain the switch closed after it has once beenclosed may be much less than that needed to close it initially, theadjustment of the light to eiiect sensitivity in response to its absencewhen cut-on"- by smoke may be such that transmuted light will beinsuflicient in the absence of smoke to cause a closure of an opencircuit switch. With a sepu arate heater forming a part of the switchstructure, this heater may be energized by closure of a circuittherethrough from some remoto point after which the light, as adjustedfor sensitivity, will be suicient to hold it closed. It is to beappreciated that where the device includes mercury as a contact element,the mercury tends to cling to the contact as that is moved away so that,having closed the circuit, the actuating element need not be heated asmuch to maintain the circuit closed.

It is an object oi the present invention to provide a new and improvedhighly sensitive heat responsive device requiring no operating or movingelements for the purpose oi compensation for ambient temperaturevariation.

It is a further object to provide a device of this charactersufliciently rugged to withstand abnormal handling and to retainadjustments made at the time of assembly.

It is an additional object to provide a novel operating structureserving to multiply to a high degree the movement of an end of anexpandable member for effecting the movement or" an operating memberwhereby the structure may he relatively small in size and yet providethe neces sary amplitude of operating movement for its contemplated use.

It is also an object to provide a device adapted to serve as theoperating mechanism of an enclosed electric switch which may beresponsive to heat energy emanating from light rays to open or close anelectric circuit.

It is another object of the present invention to provide,l in a lightactuated switch structure of this character, a second and local sourceof heat for the heat responsive member, such source comprising anelectrical resistance heater which, when energized, will effect anoperating movement of the switch Contact. Such secondary heat source maybe de-energized by means external to the present device uponpredetermined conditions and the switch thereafter retained in theposition to which the heat has moved it, by means oi. heat derived fromlight directed upon the switch actuating means.

It is also an object to provide a device which is comparatively simplein design and construction and adapted for commercial production anduse.

Other and further objects will appear as the description proceeds.

I have shown certain preferred embodiments or" my invention in theaccompanying drawings, in which- Figure 1 is a vertical view, partly insection, showing one form of construction of a two wire switch;

Figure 2 is a view similar to Figure 1 but showing a modied form ofconstruction including a three wire switch having an externallyenergized heating clement;

Figure 3 is a plan view of the construction oi Figure 2;

Figure 4 is a horizontal section showing the construction of Figure 2 onan enlarged scale; and

Figure 5 is an enlarged perspective view, partly broken away, showingthe actuating members used in both forms of the switch construction.

Referring rst to the form of construction shown in Figure l, the switchis enclosed in an evacuated bulb il having the usual exhausting andlling tube I2. The switch elements are supported on a pair of lead-inwires it and i6. In the manufacture of the device, after closing thebulb, it is exhausted and an inert gas and mercury are inserted afterwhich the filling tube l2 is closed off. The mercury, as shown at i1, isnormally trapped as a globule in a depression I3 formed in the lower endof the bulb li. The stationary contact member 20 is secured, as bywelding, to the lead-in wire 14 this contact 20 being oiset laterally toprovide room for the remaining switch elements While having its lowerend 22 extend into the globule of mercury Il. The lead-in wire I6 hassecured thereto the supporting wire 24 which is welded to a transverseend member 25, this member forming a part or" an elongated, rigidsupporting structure which includes side wall members 26 and an oppositeend member 28.

As best shown in Figure 5, the side wall member 26 is U-shaped,extending around on both sides of the end supporting members 25 and 28and being provided with stiffening corrugations 3c. The support wire 32is welded to the member 25 and carries the insulating bead 33 at itslower end. The capillary tube 35 is supported by wire 35 from theinsulating bead 33 and is insulated by that bead from the remainingstructure. The capillary tube 35 extends into the globule of mercury l1,and the tube is provided with a lateral opening 38 through which themovable contact 39 may engage the mercury.

The heat expandable member 4l has its lower end positively secured tothe lower end member 28 of the supporting structure. The main body ofthis expandable member 4! is curved in crosssection, as clearly shown inFigure 5, this curva ture serving not only to stiiien the member but,also, to provide increased area for heat absorption. The upper end 43 ofthe expandable member 4I is flat and is located closely iadjacent theiiexible blade 45. This blade 45 has its lower end positively secured,as by welding, to the upper end member 25 of the supporting structure.The upper free ends of the flat upper portion 43 of the expandablemember 4| and of the blade 45 are welded together. The actuated member46 is also welded to the upper end of portion 43 of the expandablemember 4|. In the form shown, this member 46 extends downwardly and itslower end carries the movable contact 39. It is to be noted that theupper end 43 of the expandable member 4I and the blade 45 are shown inFigure 5 with the member M in an expanded state. The position taken bythe movable contact 39 when member 4I is not expanded is shown in brokenlines.

The form of construction shown in Figures 2, 3 and 4 contains all of theelements which have been described as present in Figure l and, inaddition, contains a separate circuit connected to a third lead-in wire.The specific construction shown includes a button type base 50 havingthe lead-in wires 5l, 52 and 53 passing through thickened portions ofthe base. The lead-in wire 5I supports the xed contact member 55 whichis similar to the member 2b of Figure 1. The lead-in wire 52 supports aninterior Wire 51 similar to the wire 24 of Figure l, but the wire 51has'a secondary support wire 59 welded thereto, this wire 59 supportingan insulating bead 60. The insulating bead 60 is also secured to thethird lead-in wire 53 which protrudes below it. From this end of wire53, a resistance heating element 6d is -connected in series with thewire 51 by being welded to the latter Wire at 65.

The tubular glass envelope (il of the form of construction of Figures 2,3 and i is provided wit an external mirrored surface 69 which, as bestshown in Figure 4, is designed to reflect rays of light against thearcuate or rounded surface of the expandable member 4i at the focalpoint. In the form of construction shown in Figure l, the mirror is notused, the light impinging directly on the member H, as indicated by thearrows in Figure l. If desired in this form, a cylindrical or sphericallens may be interposed between the source of light and the glassenvelope to focus the light rays upon the expandable member. While theparticular form of construction of the base and enclosing bulb forms nopart of the present invention, it has been found that the button typebase shown in Figure 2 affords a finished switch shorter in length andmore adaptable to compact installation than that type of constructionshown in Figure 1.

The various elements of the supporting structure, including the endmembers 25 and 28 and the intermediate connecting U-shaped member 26,are formed of a metal or zalloy having a high temperature coefficient ofexpansion and prefstructure multiplies greatly the movement imi" partedby the expansion of the member 4|. The alloy used is also quite rigidand, as specific examples, the supporting member 26 may be formed ofmetal .003 inch in thickness, while the upper and lower members 25 and28 may have crosssectional dimensions on the order of .065 inch by .125inch. The embossed ribs 30 serve to add to the rigidity of thestructure.

It is to be noted that the open end of the U- shaped member 26 is towardthe expandable member 4| and that that member is spaced somewhat awayfrom the support. This reduces heat transfer and, in the form ofconstruction shown in Figure 2 where the resistance heater element 64 isused, it keeps the supporting structure away from the heater.

The current carrying wires `and the supporting members for the capillarytube 35 may be formed of iron, and the contact point 39 carried by theactuated member 65 may be formed of platinum,

6 which is readily wetted by mercury, thus insuring a uniform separationfrom the mercury throughout repeated operations. The electricalresistivity is substantially that of the iron wire to which it issecured.

The length of the upper flat portion 43 of the expandable member 4l andthe length of the movable portion of the flexible blade 45 are kept to aminimum commensurate with their ability to be flexed within the elasticlimits of the metal from which they are formed throughout the expandablelimits of the expandable member il. It has been found in actual practicethat, by tensioning the expandable member 4l and the flexible blade 45the proper amount, they can be caused to lie substantially against eachother at normal ambient temperatures so that, upon expension of theexpandable member, movement of the joined upper ends of the two memberstakes place with little or no lost motion. The ilexing action takesplace about the upper frame end support 25, the upper corner thereofserving as a fulcrum. v

By making the flexible blade 45 and flat portion 43 of the expandablemember as short as possible without either member taking -a setthroughout the intended range of temperature changes and yet not soshort that the blade tends to act as a restraining influence on themovement of the free end of the expandable member, a maximum of angulartravel can be' obtained at the line where the free ends of these twomembers are joined. By having the two flat surfaces in contact with eachother, or Substantially so, a slight curling action results at theirfree ends upon expansion of the expandable member to augment the angulartravel obtained so that -a very high degree of movement is imparted tothe contact arm or actuated member secured thereto. With the expandablemember IH and the blade 45 under very little tension any expansiontaking place in the expandable member results in an immediate pushingaction to the right, as clearly shown in Figure 5. A metal is preferablyused which is a poor heat conductor so that the heat from the expandablemember 4i is not lost to the blade 45 and expansion is mainly confinedto the member 4I. It is to be noted that only the small upper portion 43of the member 4l is in contact with the blade d5.

In the form of construction shown in Figures 2, 3 and 4, the heaterelement 64 is connected between lead-in wires 52 and 53, while theswitch closes the normally open circuit between lead-in wires 5| and 52.In one specific form of construction, a heater 64 drawing aboutone-sixth of an ampere effected a switch closure in fifteen seconds andan opening of the switch circuit thirty seconds after the heater circuithad been opened. In this specific embodiment, when the device wasexposed to the light from a fluid fuel burner flame, applied asindicated by the arrows of Figure 4, the switch contact was closed iniive seconds and the switch opened in the same length d of time afterthe burner flame was out. With a metal of low heat conductivity used asspecified herein, the device was tested under ambient temperatureconditions varying from 35 F. to 206 and the variation in time responseto closure vconstructed to insure transmission of a minimum of light andheat to; the supporting structure. In the form of construction yshown inFigure 1,

the supporting structure is entirely shielded from the direct light raysby the member M when the device is properly oriented towards the lightsource. In the form of construction of Figures 2 to l with the mirror,the light is concentrated on member 4I so that the light reaching thatelement is very substantially greater than light or heat rays impingingupon the supporting structure which presents a narrow face toward thelight source.

While I have shown certain preferred embodiments of my invention, theseare to be understood to be illustrative only as it is capable oi changeand variation to meet differing conditions and requirements, and Icontemplate such modifications as come within the spirit and scope ofthe appended claims. As one example of modication, the movable switchcontact may be so related to a iixed contact including a meniscus ofmercury that the movable contact may be norbeing substantially shorterthan the expandable l member and extending parallel to said member, thefree ends of said member and blade being connected together, and anactuated member se cured to said point of connection, the major portionof the expandable member being relatively rigid with that portion ofsaid member adjacent and parallel to the flexible blade being relativelyflexible.

2. A heat responsive actuating device comprising a transparent,impervious bulb enclosing the operating parts, a supporting structure, aheat expandable member having one end secured to the supportingstructure, said member being of an area suicient to cover the adjacentiace of the supporting structure and extending beyond than theexpandable member and extending parallel to said member, the free endsof said member and blade being connected together, said supportingstructure and expandable member being both formed of the same metal,said metal having a high coecient of expansion and low thermalconductivity, and an actuated member secured to said point ofconnection.

3. A heat responsive device comprising a transparent, impervious bulbenclosing the operating parts, a rigid frame having top and bottomsupporting means, a flexible blade having one end secured to the topsupport with its free end extending thereabove, an expandable andcontractible member having one end secured to the bottom support and afree end extending beyond the top supporting member, the free ends ofthe flexible blade and expandable and contractible member being securedtogether, the portion of the expandable and contractilble memberadjacent its free end providing a dat and flexible section comparable insize to the flexible blade, the lengths of the flat section and exibleblade being no greater than that required to prevent movement theretobeyond their respective elastic limits throughout the normal expandablerange of the expandable member, and means secured to the securedtogether free ends to transmit movement imparted thereto to a part to beactuated.

4. A heat responsive device comprising a transparent, impervious bulbenclosing the operating partsy a rigid frame having top and bottomsupporting means, a flexible blade having one end secured to the topsupport with its free end extending thereabove, an expandable andcontractible member having one end secured to the bottom support and afree end extending beyond the top supporting member, the free ends ofthe flexible blade and expandable and contractible member being securedtogether, the portion of the expandable and contractible member adjacentits free end providing a flat and flexible section comparable in size tothe flexible blade, the remainder of the length of the expandable memberbeing stiffened by an arcuate crosssection, the lengths of the flatsection and flexible blade being no greater than that required toprevent movement thereto beyond their respective elastic limitsthroughout the normal expandable range of the expandable member, andmeans secured to the secured together free ends to transmit movementimparted thereto to a part to be actuated.

5. A heat responsive device comprising a transparent, impervious bulb'enclosing the operating a rigid frame having top and bottom supured tothe top support with its irse end exing thereabove, an expandable andcontractible member having one end secured to the bottom support and afree end extending beyond the top supporting member, the free ends ofthe exible blade and expandable contractible member being securedtogether, the portion of the expandable and contractible member adjacentits free end providing a dat ilexible section comparable in size to theflexible blade, the lengths of the flat section and flexible blade beingno greater than that required to prevent movement thereto beyond theirrespective elastic limits throughout the normal expandable range of theexpandable member, and means secured to the secured together free endsto transmit movement imparted thereto to a part to be actuated, the areaof the expandable member as ved from the side of said member oppositethe rigid lirame being substantially the same as that of the frame whenviewed irom the same direction.

A heat responsive device comprising transparent, impervious bulbenclosing the operating parte, an elongated rigid supporting structure,a heat expandable member having one end secured adjacent one end of thesupporting structure, said member extending beyond the other end or" thesupporting structure, a flexible blade secured adjacent the second endor the supporting structure and extending away from said structure parnallel to that portion of the heat expandable member extending beyondsaid structure, adjacent free ends 0i the expandable member and theflexible member being secured together, an actuated member securedadjacent said last named point of connection, the major portion of theexpandable member being arcuate in cross-section to stiffen that portionof the member and to proporting means, a flexible blade having one endvide increased surface area, and means for concentrating a beam ofradiant energy on said expandable member.

7. A heat responsive actuating device comprising a transparent,impervious bulb enclosing the operating parts, a supporting structure,operating member and an actuated member all made of the same material,said supporting structure being rectangular with projecting armsextending from opposite extremities thereof contiguous with the shortdimensioned ends of the support for mount ing the operating member inspaced parallel relationship with one of the longest sides of thesupporting structure, said operating member consisting of a thin bladesecured at one end to one of the support arms with its free endextending beyond the other of said support arms, said actuated memberconsisting of a thin nexible blade having one end secured to the otherarm and extending therefrom parallel and adjacent to the extended freeend of the operating member, the free end of both being connectedtogether to cause a flexing of the actuated member upon the longitudinalexpansion of the operating member as a result of a diilerential intemperature being established between the operating member and that ofthe rest of the device.

8. A heat responsive actuating device comprising a transparent,impervious bulb enclosing the operating parts, an elongated, U-shaped,rigid supporting structure, a heat expandable member, the supportingstructure and the heat expandable member both being formed of metalhaving a high coeicient of expansion and low thermal conductivity, saidexpandable member having one end secured adjacent one end of thesupporting structure, said member extending substantially parallel toand spaced apart from the lateral open end of the supporting structureand beyond the other end of the supporting structure, said member havingvan area suiiicient to cover said open end of the supporting structure,a flexible blade secured adjacent the second end or" the supportingstructure and extending parallel to the expandable member, adjacent freeends of the expandable member and the ilexible lade being connectedtogether, and an actuated member secured adjacent said last named pointof connection.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,777,272 Beam Sept. 30, 1930 2,051,915 Mautsch Nov. 24, 19362,083,317 Dallenbach June 8, 1937 2,170,748 Eaton Aug. 22, 19392,185,436 Gordon, Jr. Jan. 2, 1940 2,251,003 Rich July 29, 19412,255,169 Ireland Sept. 9, 1941 2,272,021 Riche Feb. 3, 1942 2,318,598McCabe May 11, 1943 2,392,065 Rodgers Jan. l, 1945 FOREIGN PATENTSNumber Country Date 104 Great Britain Jan. 13, 1859

